Old 05-29-2019, 10:15 AM
jamaca85 jamaca85 is offline
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Default Exhaust manifold flange size

What the biggest size pipe that can be mounted on a stock d ports exhaust manifold flange. Looking at the ram air type manifolds. Thanks

1970 firebird, 468, e heads,
Old 05-29-2019, 12:40 PM
form74's Avatar
form74 form74 is offline
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Join Date: Jun 2002
Location: Glen Ellyn, Illinois
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I have the RamAir 2.5 manifolds with these down pipes in the attachment, which allows 3 inch exhaust all the way to the tail pipes.


74 Formula
469, 6X-4's, 72 Intake, Ramair Manifolds.
3 inch exhaust with x-pipe
Custom Roller Cam, 1.52 Roller Rockers
Quadrajet done by Cliff
3:42 gears

12.145 @ 108.73
12.163 @ 111.55
12.170 @ 111.01

Old 05-30-2019, 06:25 AM
jamaca85 jamaca85 is offline
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1970 firebird, 468, e heads,
Old 05-30-2019, 09:07 AM
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Sirrotica Sirrotica is offline
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Join Date: Jan 2005
Location: South Charleston Ohio
Posts: 5,677

With log manifolds and 2 bolt flanges 2 1/4" is usually about as big as you can go.

The RA manifolds have larger flange areas enabling 2 1/2" if you enlarge the center hole in the flange.

There is a way to adapt up to 3" pipes using header collector flanges adapted to the 2 or 3 hole flanges, requires welding and fab skills. Basically the old flange pattern is used to build a plate that is first bolted to the manifold and then has the 3 hole header collector flange pattern on the 3 inch pipe that is then bolted to the adapter plate.

Way back years ago, on the 67 GTO in my middle signature picture I built adapters to adapt the 3 hole Pontiac RA head pipes to driveshaft tubing (3 1/2 inch OD) that dumped at the rear axle. The seat of the pants dyno was feeling the improvement...LOL

Brad Yost
1973 T/A 4 SALE (SOLD)
2005 GTO
1984 Grand Prix

100% Pontiacs in my driveway!!! What's in your driveway?


Last edited by Sirrotica; 05-30-2019 at 09:26 AM.
Old 06-01-2019, 02:54 PM
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bill ryder bill ryder is online now
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Posts: 1,680

I also have a complete 3" system from RamAir with X pipe and electric cut outs. Fits like a glove. Sounds GREAT..



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